CN102324858B - Voltage transforming rectifier with dual functions of voltage stabilization and harmonic injection - Google Patents

Abstract

The invention relates to a transformer rectifier with dual functions of voltage stabilization and harmonic injection, which belongs to the field of power electronic equipment. It includes a phase-shifting transformer 1, a three-phase bridge rectifier circuit 2, a three-phase bridge rectifier circuit 3, a balance reactor 4, a switching inverter circuit 5, a single-phase rectifier bridge 6, a high-frequency transformer 7, a controller 8 and an inductor 9. Its characteristics are: through the switching inverter and high-frequency transformer, the triangular wave current is injected into the balance reactor, so that the current waveform at the input terminal of the phase-shifting transformer is closer to sinusoidal, which is conducive to improving the power factor of the entire equipment and ensuring the "cleanness" of the public grid ". The voltage stabilizing circuit includes a switching inverter circuit, a single-phase rectifying bridge and a high-frequency transformer, so that the transformer rectifier has a stable output voltage under different loads, which is beneficial to improving the load capacity of the system. Compared with the transformer rectifier adopting independent voltage stabilizing circuit and harmonic injection circuit, adopting the transformer rectifier of the present invention reduces the number of components and parts, reduces the complexity of the system, and has low input current harmonics and stable output voltage accuracy With high advantages, it is suitable for medium and high power rectification occasions in the aviation industry and national production.

Description

A Transformer Rectifier Combining Dual Functions of Voltage Stabilization and Harmonic Injection

technical field

The invention relates to a transformer rectifier with dual functions of voltage stabilization and harmonic injection, in particular to a transformer rectifier with adjustable output voltage and low input current harmonic applications. It belongs to the field technology of power electronic equipment.

Background technique

Transformer rectifiers are widely used in aerospace, electrolytic plating, rail transit, wind power generation and other occasions that require medium and high power rectification conversion. A transformer rectifier is generally composed of a phase-shifting transformer, multiple three-phase full-bridge rectifier circuits, and a balance reactor. Through the phase-shifting transformer, the input currents of multiple three-phase full-bridge rectifier circuits are staggered and superimposed in a certain phase, so that the input side current is closer to the sine wave, and the purpose of reducing the harmonic content of the input current is achieved. Each rectifier circuit can be output in parallel or directly in series through balanced reactors to obtain a DC output voltage with a ripple corresponding to the pulse number. The voltage varies with the input side voltage, and generally has no voltage stabilization function. According to the number of pulses, there are 6, 12, 18, 24 and other multi-pulse transformer rectifiers. As the number of pulses increases, the harmonics of the input current decrease correspondingly, but at the same time the complexity of the circuit increases accordingly.

As transformer rectifiers are more and more widely used, the requirements for input and output performance of rectifiers are also getting higher and higher in many occasions. It is hoped that the transformer rectifier has a small input current harmonic and can realize the function of voltage stabilization. For the reduction of input current harmonics, it is generally to connect the filter link at the input terminal or increase the pulse number of the transformer rectifier. The structure of the main circuit and the transformer is complicated and the cost is increased. The method of harmonic injection can effectively reduce the input current harmonics. For the stability of the output voltage, the basic idea is to connect an adjustable voltage source in series as the post-stage circuit of the transformer rectifier. However, when the above two functions are required to be realized at the same time, if the harmonic injection circuit and voltage stabilization circuit are directly added to the traditional transformer rectifier, the number of components will inevitably be greatly increased, and the harmonic injection circuit needs an auxiliary source, which makes the circuit complicated. The degree increases, the volume weight increases, and the reliability decreases.

Therefore, it is necessary to seek a new type of transformer rectifier with high reliability that can realize the dual functions of voltage stabilization and harmonic injection, simplify the circuit structure and reduce the number of components to a certain extent.

Contents of the invention

1. Purpose of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a transformer rectifier device with dual functions of output voltage stabilization and reduction of input current harmonic content through harmonic injection method, so as to solve the problem of traditional transformer rectifiers due to the direct increase of the voltage stabilization circuit. The disadvantages of circuit complexity, greatly increased volume and weight, and reduced reliability brought about by harmonic injection circuits.

2. Technical solution

In order to achieve the above-mentioned purpose of the invention, the main circuit of the transformer rectifier with dual functions of voltage stabilization and harmonic injection includes a phase-shifting transformer, two three-phase full-bridge rectifier circuits, a voltage stabilization circuit and a harmonic injection circuit. The harmonic injection circuit is composed of a switch inverter circuit, a high frequency transformer, a balance reactor and an inductance, and the voltage stabilizing circuit is composed of a switch inverter circuit, a high frequency transformer and a single-phase rectifier bridge. Wherein, the voltage stabilizing circuit and the harmonic injection circuit together include a switching inverter circuit and a high frequency transformer. For the harmonic injection circuit, current hysteresis control technology is used to control the current waveform in the harmonic injection circuit to be a triangular wave. Through the action of the rectifier and the phase-shifting transformer, the triangular waves with different phase relationships are superimposed in a certain proportion to obtain the input terminal current of the phase-shifting transformer. , its waveform is closer to a sine wave, and the harmonic content is greatly reduced to achieve the purpose of reducing the input current THD; for the voltage stabilizing circuit, because the current hysteresis control is realized, the controller will generate a series of driving signals to drive the switch inverter The power switching tube of the transformer circuit will generate a series of positive and negative alternating voltage square waves on the primary side of the high-frequency transformer. In order to realize the voltage stabilization function, a step-by-step voltage regulation method is adopted. This method reduces the switching voltage of the single-phase rectifier bridge. The frequency reduces the switching loss, and the control is simple, feasible and accurate. In the present invention, when the voltage stabilization and harmonic injection circuit fails, the transformer rectifier with dual functions of voltage stabilization and harmonic injection can be operated as a traditional transformer rectifier, so it has a certain redundancy and improves reliability.

The double-function voltage transformer rectifier of the fusion voltage stabilization and harmonic injection of the present invention, through the fusion of the voltage stabilization circuit and the harmonic injection circuit, and adopts the step-by-step voltage regulation control method, realizes the voltage stabilization function while realizing the harmonic injection function , so that the transformer rectifier can greatly reduce the harmonic content of the input current without increasing the pulse number, improve the power factor of the input terminal, and at the same time make the output voltage stable at a predetermined target under different loads Voltage value, improve the load capacity of the transformer rectifier.

3. Beneficial effects

The transformer rectifier with dual functions of voltage stabilization and harmonic injection of the present invention is a transformer rectifier related to aerospace, electrolytic plating, rail transit, wind power generation and other medium and high power applications, and has the following advantages: (1) Without increasing the pulse number of the transformer rectifier, the harmonic content of the input current of the transformer rectifier is reduced, and the power factor at the input end is improved, thereby reducing the volume of the input filter and reducing the harmonic flow band in the public power grid. (2) Through the function of the voltage stabilizing circuit, the output voltage can have a stable voltage output under different load conditions, and the load capacity of the system can be improved; (3) The two functions of voltage stabilizing and low harmonic injection are in the Simultaneously realized in a fused simplified circuit, the circuit structure is simpler, the number of components is less, the complexity is reduced, and the reliability is increased; (4) The voltage regulation function is realized by a hierarchical voltage regulation method. It is a combination of coarse adjustment and fine adjustment, which avoids the limitation of the duty cycle variation range, and under the condition of realizing voltage regulation accuracy, reduces the switching frequency of the rectifier bridge, reduces switching losses, and improves system efficiency to a certain extent.

Description of drawings

Fig. 1 is a structural block diagram of the main circuit of the present invention.

Fig. 2 is a schematic diagram of the topological structure of the main circuit part of the present invention.

Fig. 3 is a schematic diagram of the equivalent circuit topology of the harmonic injection of the present invention.

Fig. 4 is a schematic diagram of the working state waveform of the current hysteresis loop control of the harmonic injection circuit in the present invention.

Fig. 5 is a schematic diagram of waveforms of the step-by-step voltage regulation mode of the voltage stabilizing circuit in the present invention.

In Fig. 1: the input terminals U, V, and W of the phase-shifting transformer 1 are connected to the three-phase AC power supply, and in Fig. 2 and 3 are two sets of three-phase full-bridge rectifier circuits with the same specifications; in Fig. 2: the balance reactor 4 The input terminal voltages U _d1 and U _d2 are the output voltages of the three-phase full-bridge rectifier circuits 2 and 3 respectively, N _p and N _x are the turns of the primary side and the secondary side of the balance reactor respectively, and N ₁ , N ₂ and N ₃ are the turns of the primary and two secondary windings of the high-frequency transformer respectively, C ₁ and C ₂ are the output of the balanced reactor and the final output filter capacitor after voltage regulation, U _o is the final output voltage; In Figure 3: U _C1 · N ₃ /N ₁ is the equivalent converted voltage value of the voltage U _C1 across the capacitor C ₁ on the secondary winding N ₃ of the high-frequency transformer; in Figure 4: (a) is the current hysteresis control (b) is the waveform on the secondary winding N ₃ of the high-frequency transformer, (c) is the equivalent waveform on the secondary winding N ₃ of the high-frequency transformer obtained by using the area equivalent theorem; in Fig. 5 : (a) is the equivalent waveform on the secondary winding _N2 of the high-frequency transformer, (b) is the output voltage U _r1 waveform diagram of the single-phase rectifier bridge when the drive signal of the switching tube of the single-phase rectifier bridge is divided by 1, (c ) is the waveform diagram of the output voltage U _r2 of the single-phase rectifier bridge when the driving signal of the switching tube of the single-phase rectifier bridge is divided by 2.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

This example takes the input of three-phase 115V/400Hz AC and 12-pulse transformer rectifier as an example for illustration. The block diagram of the main circuit structure of the transformer rectifier with dual functions of voltage stabilization and harmonic injection is shown in Figure 1, and its characteristic is that its circuit structure consists of a phase-shifting transformer 1, a three-phase full-bridge rectifier circuit 2, and a three-phase full-bridge rectifier circuit 3. Balance reactor 4, switch inverter circuit 5, single-phase rectifier bridge 6, high-frequency transformer 7, controller 8 and inductor 9. The phase-shifting transformer 1 is a transformer with a phase shift of 30°. Its input terminal is connected to a three-phase 115V/400Hz alternating current, and the phase difference of the two three-phase outputs is 30°. The three-phase full-bridge rectifier circuit is connected in parallel through the balance reactor 4, and the output end of the balance reactor is connected in parallel with the switching inverter circuit 5. The switching inverter circuit 5 is composed of four switching tubes Q1-Q4 and four diodes, the switching tube Q1 and the switching tube Q3 are connected in series in forward direction to form a bridge arm, and the switching tube Q2 and the switching tube Q4 are connected in series in forward direction to form another bridge arm. The two bridge arms are connected in parallel in the same direction to form a bridge circuit, and the output lines are respectively drawn out at the junction of Q1 and Q3 and the junction of Q2 and Q4. For the connection of diodes, each diode corresponds to a switch tube, and is connected in antiparallel with the switch tube to provide an energy feedback channel for the voltage stabilizing circuit. The output of the switching inverter circuit 5 is connected to the primary winding of the high-frequency transformer 7, the second secondary winding of the high-frequency transformer is connected to the secondary winding of the balance reactor 4 through the inductance 9, and the first secondary winding is directly connected to the single-phase The rectifier bridge 6 is connected. The single-phase rectifier bridge 6 is composed of four switching tubes Q5~Q8, the switching tubes Q5 and Q6 are connected in series in the forward direction to form a bridge arm, the switching tubes Q7 and Q8 are connected in series in the forward direction to form another bridge arm, and the two bridge arms are connected in parallel in the forward direction A bridge circuit is formed, and the entire single-phase rectifier bridge is serially connected into the circuit. One end of the single-phase rectifier bridge is connected to the balance reactor, and the other end is taken as the final output end. The connection between the switching tubes Q5 and Q6 and the connecting points between the switching tubes Q7 and Q8 are respectively connected to the first secondary side of the high-frequency transformer 7. both ends of the winding. The controller 8 samples the voltage U C1 at the output end of the balance reactor 4 (that is, the capacitor _{C 1} ), the current i _x on the inductor 9, and the final output voltage U _o , and generates the voltages of the switching tubes Q1 to Q8 according to the set operation relationship. Drive signal, so as to realize current hysteresis control and graded voltage regulation control.

Working principle of the present invention is:

As mentioned above, the voltage stabilizing circuit and the harmonic injection circuit are integrated into a whole circuit. In order to facilitate the analysis of its working principle, the circuit can be equivalently separated. Because the voltage U _C1 at both ends of the capacitor _C1 passes through the switch inverter circuit and then passes through the high-frequency transformer to transform the output effect, and the effect of the voltage U _C1 at both ends of the capacitor _C1 passes through the high-frequency transformer and then passes through the switch inverter bridge. are the same, so the original harmonic injection circuit can be equivalent to the circuit topology diagram shown in Figure 3. As shown in Figure 3, the controller samples the output voltage U _C1 of the balanced reactor and the current _ix on the inductor through the signal sampling circuit, and compares the sampled real-time current _ix signal with the maximum value _{ia ( max)} is compared with the minimum value i _a(min) , when the inductor current i _x reaches i _a(max) , the switching states of Q1~Q4 in the switching inverter are changed, so that the direction of the output voltage is opposite to that of the current, so that The inductor current _ix decreases; when it decreases to the minimum value i _a(min) , the switching states of Q1~Q4 in the switching inverter are changed again, so that the output voltage and the direction of the current are in the same direction, so that the inductor current _ix Increase. Among them, the determination of i _a(max) and i _a(min) values depends on the indicators required by the system. Its current waveform diagram is shown in Figure 4(a). According to the above control method, the inductor current i _x can be made into a triangular wave. When the peak value of the target current waveform i _a is half of the final output current, the harmonic content of the input current can be reduced. The best effect can greatly reduce the total harmonic distortion rate of the input current, ensuring that the input current THD of the twelve-pulse transformer rectifier meets the standards of various applications. The second secondary output waveform of the high frequency transformer in the circuit shown in Fig. 2 is shown in Fig. 4(b). In actual control, in order to prevent the switching tubes on the same bridge arm from being turned on at the same time, the driving signal generated by the controller must be processed by the dead time control unit before it can drive the switching tubes in the switching inverter, so the actual waveform of U _N3 It is zero within a certain period of time between positive and negative pulses.

In this embodiment, it can be obtained from the waveform in Figure 4(b): when U _N3 is positive, the switching tubes Q2 and Q3 in the switching inverter circuit are turned on at the same time, at this time, the voltage direction is the same as the current direction, and the inductor current i _x rises; when U _N3 is negative, the switching tubes Q1 and _Q4 in the switching inverter circuit are turned on at the same time. The turn-on and turn-off of tubes Q1-Q4 form a PWM voltage waveform. In order to facilitate the description of the control method of the voltage stabilizing circuit, using the area equivalent principle, the PWM waveform in Figure 4(b) can be equivalent to the square wave waveform in Figure 4(c), and from Figure 4(b) The law of current hysteresis control can be obtained. In the interval where the target current waveform i _a rises, the area of the positive pulse in the PWM waveform of U _N3 is greater than the area of the negative pulse. Similarly, in the interval where the target current waveform i _a falls, The area of the negative pulse in the PWM waveform of U _N3 is larger than the area of the positive pulse, as shown in Figure 4(c), within t ₁ ~ t ₂ , because the waveform of the target current i _a drops, so the negative pulse of the PWM waveform of U _N3 The area is greater than the area of the positive pulse, so it can be equivalent to a square wave with an amplitude of -U _eq . Since the target current waveform i _a is a periodic triangular wave, the current falling time is equal to the rising time. In a stable working state, the equivalent The positive and negative pulse width of the voltage square wave is equal and the amplitude is the same. This equivalent method can make the high-frequency voltage pulse equivalent to a voltage pulse with a greatly reduced frequency, which is conducive to reducing the frequency of the driving signal of the switching tube in the single-phase rectifier bridge and reducing the switching loss.

In this embodiment, due to the effect of the high-frequency transformer, the waveform generated on the first secondary winding _N2 in the high-frequency transformer is the same as the voltage waveform on the second secondary winding _N3 , denoted as U _N2 , which The amplitude is U _eq ·N ₃ /N ₂ , as shown in Fig. 5(a). The equivalent waveform of U _N2 is also a square wave waveform with equal positive and negative pulse widths and the same amplitude. In order to generate a positive or negative DC voltage at the output end of the single-phase rectifier bridge, it is realized by a step-by-step voltage regulation method. The basic idea of step-by-step voltage regulation is: take the number of positive pulses in a period of time according to the frequency division method to take part of the pulse number, and the voltage values obtained under different frequency division numbers are graded, which can realize rough adjustment of voltage , and then in a certain frequency division state, adjust the duty cycle of the drive signal to achieve fine-tuning of the voltage. In the process of controlling the switching tubes in the single-phase rectifier bridge by using step-by-step voltage regulation, the main and auxiliary switching tubes work mode is implemented, that is, in the process of step-up voltage regulation, one main switch tube is normally on, and in the process of step-down voltage regulation , the other main switching tube is normally on, and the other two auxiliary switching tubes are turned on in turn no matter in the step-up or step-down voltage regulation process. This working mode reduces the switching loss again to a certain extent.

The working principle of the step-by-step voltage regulation control method will be further described in detail below with the waveform diagram in FIG. 5 and the circuit structure topology diagram in FIG. 2 .

This embodiment is a twelve-pulse transformer rectifier. When the frequency of the input alternating current is 400 Hz, the frequency of the triangular wave current to be injected into the harmonic injection circuit is 2400 Hz, and the high-frequency transformer can be obtained by analyzing the aforementioned current hysteresis link control method The equivalent waveform frequency of the voltage U _N2 on the secondary side N ₂ is also 2400 Hz.

When the voltage U _C1 across the capacitor _C1 is less than the predetermined output voltage, step-up and voltage regulation are required. As shown in Figure 5(b), when the driving signal of the switching tube in the single-phase rectifier bridge is divided by 1, that is, 2400Hz, the output voltage of the single-phase rectifier bridge is U _r1 , where the waveform of U _r1 is taken as U _N2 All positive pulses in the waveform, this is the maximum adjustment value U _eq ·N ₃ /(2·N ₂ ) of the boost regulator. Combining with the circuit structure in Figure 2, it can be concluded that: within 0~ _t1 , the switching tube Q8 and Q5 in the single-phase rectifier bridge are turned on, so that the waveform of U _r1 is positive; within _t1 ~ _t2 , the switching tube Q8 and Q5 Q7 is turned on, making the U _r1 waveform zero. As shown in Figure 5(c), when the driving signal of the switching tube in the single-phase rectifier bridge is divided by 2, that is, 1200Hz, the output voltage of the single-phase rectifier bridge is U _r2 , where the waveform of U _r2 is taken as U Half of the number of positive pulses in _{the N2} waveform, combined with the circuit structure in Figure 2, it can also be obtained: within 0 ~ t ₁ , the switch tube Q8 and Q5 in the rectifier bridge are turned on, so that the U _r2 waveform is positive, and at t From ₁ to _t4 , the switching tubes Q8 and Q7 are turned on, so that the waveform of U _r2 is zero. Combining the working state of 1 frequency division and 2 frequency division, it is similar to the state of n frequency division. It can be seen that Q8 is a normally-on switch tube, and Q5 and Q7 are turned on in turn.

When the voltage U _C1 across the capacitor _C1 is greater than the predetermined output voltage, step-down regulation is required. In the step-down voltage regulation process, it has a similar relationship with the step-up voltage regulation, the difference is that the voltage output by the rectifier bridge is a negative pulse sequence, and the switch tubes that are turned on are also different. When the driving signal of the switch tube in the single-phase rectifier bridge is divided by 1, within t ₀ ~ t ₁ , the switch tube Q6 and Q7 in the single-phase rectifier bridge are turned on, so that the waveform of U _r1 is negative; during t ₁ ~ t ₂ Inside, the switch tubes Q6 and Q5 in the single-phase rectifier bridge are turned on, so that the waveform of U _r1 is zero. It can be seen that Q6 is a normally-on switch tube in the step-down voltage regulation, and Q5 and Q7 are turned on in turn. According to the above relationship, it can be concluded that in the process of step-up voltage regulation and step-down voltage regulation, the switch tubes Q8 and Q6 in the single-phase rectifier bridge are always turned on respectively, which is the main switch tube in the working mode of the main and auxiliary switch tubes. , and the switch tubes Q5 and Q7 are determined by the frequency division number to turn on the time, so they are auxiliary switch tubes.

According to the above rule of 1 frequency division and 2 frequency division, and so on, it can be concluded that the relationship between the number of frequency division and the number of pulses within a period of time (taking one second as an example) is shown in Table 1 below:

Table 1 The relationship table between frequency division number and pulse number

frequency division 1 2 3 4 5 n Number of pulses 2400 1200 800 600 480 2400/n

As shown in Table 1, different voltage pulse numbers correspond to different levels of voltage values. The frequency division number is determined according to the difference between the voltage U _C1 at both ends of the capacitor C ₁ and the final output target voltage U _o , and the adjustment is made within a rough range. Voltage, and the smaller the voltage regulation value, the larger the frequency division number, the lower the switching frequency of the switching tube in the rectifier bridge, the smaller the switching loss, which is conducive to improving efficiency. In order to further fine-tune the voltage, the duty cycle control is adopted, as shown in the waveform in Figure 5(c), when the driving signal of the switching tube of the single-phase rectifier bridge is divided by 2, the time _t4 remains unchanged, and the change of t ₁ , thereby changing the duty cycle of the driving signal D=t ₁ /t ₄ , so by reducing the duty cycle D, the continuous adjustment of the voltage within the frequency division by 2 and the frequency division by 3 can be realized. When it is extended to all frequency division numbers, the fine adjustment of voltage can be realized within the range of all frequency division numbers, and the combination of coarse adjustment and fine adjustment makes the output voltage stable at a predetermined value with high precision. The step-by-step voltage regulation method solves the problem that high-precision fine-tuning cannot be realized due to too small duty cycle.

The above embodiment is only a specific implementation circuit principle diagram of the present invention, and does not limit the scope of protection of the present invention. Any equivalent transformation circuit based on the present invention belongs to the protection scope of the present invention.

Claims (2)

1. a vertoro that merges voltage stabilizing and harmonic wave injection dual-use function, is characterized in that comprising phase shifting transformer, two three-phase bridge rectification circuits, voltage stabilizing circuit and harmonic wave injection circuits; Described harmonic wave injection circuit is comprised of switching inverter circuit, high frequency transformer, interphase reactor and inductance, adopts Hysteresis Current Control Strategy to realize the harmonic wave function of injecting; Described voltage stabilizing circuit is comprised of switching inverter circuit, high frequency transformer and single-phase rectification bridge, adopts the stepped voltage regulation mode to realize its voltage regulation function; Voltage stabilizing circuit and harmonic wave injection circuit comprise switching inverter circuit and two parts of high frequency transformer jointly, and the circuit of two standalone features is merged, and realize that voltage stabilizing and harmonic wave inject two kinds of functions simultaneously; High frequency transformer comprises three windings, its former limit connecting valve inverter circuit; First secondary winding access single-phase rectification bridge forms voltage stabilizing circuit; Second secondary winding forms the harmonic wave injection circuit through inductance access interphase reactor secondary.

2. merge according to claim 1 the vertoro that voltage stabilizing and harmonic wave inject dual-use function, it is characterized in that: voltage stabilizing circuit adopts the stepped voltage regulation method to realize pressure regulation, maximum range of regulation is divided into to some intervals by the frequency division mode, the magnitude of voltage of adjusting when needs is a certain when interval, determine as calculated the divider ratio of switching tube driving signal in single-phase rectification bridge, realize coarse adjustment, and then switching tube drives the duty ratio of signal to realize fine setting in this frequency downconverts joint single-phase rectification bridge, make output voltage with high-accuracy stable in predetermined value.

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